Spectroscopy of the bright optical counterparts of X-ray sources in the direction of M 31

¹ University of Crete, Department of Physics, PO Box 2208, 71003, Heraklion, Greece e-mail: paolo@physics.uoc.gr
² IESL, Foundation for Research and Technology, 71110, Heraklion, Greece
³ Max-Planck-Institut für extraterrestrische Physik, 85741 Garching, Germany

Received: 15 May 2009
Accepted: 17 July 2009

Abstract

Context. A recent survey of the Local Group spiral galaxy M 31 with XMM-Newton yielded a large number of X-ray sources.

Aims. This is the second in a series of papers with the aim of identifying the optical counterparts of these X-ray sources.

Methods. We have obtained optical spectra for 21 bright optical counterparts of 20 X-ray sources in the direction of M 31, using the 1.3-m Skinakas telescope in Crete, Greece.

Results. For 17 of the 20 X-ray sources, we have identified the optical counterpart as a normal late type star (of type F or later) in the foreground (i.e. in the Milky Way). For two more sources, there were two possible optical counterparts, in each case, while two more objects have X-ray properties that are not compatible with the spectral characteristics of late type non-flaring stars.